When a ray of light comes into contact with a drugged drink, it is slightly altered The sensor can pick up that subtle change and sound an alarm - perhaps a beeping sound or a small flashing light, the researchers say. The sensor can operate with only 10 microlitres of liquid.

Early tests are very promising, but they're early tests - so in the meantime, you'll still need to keep an eye on your drink, just to be safe.